Joining Structural Members by Friction Welding

ABSTRACT

An apparatus and method for joining structural members to form preforms and structural assemblies are provided. The structural members are positioned so that joining surfaces thereof define an angled aperture, such a slot or frustoconical bore, that receives a corresponding joining member. The joining member is urged into the aperture against the joining surfaces and moved, for example, by oscillating or rotating the joining member, to friction weld the joining member to the structural members. Each structural member can include a clamping portion that is received by a clamping device that prevents the aperture from opening as the joining member is urged into the aperture. A gripping portion of the joining member and the clamping portions of the structural members can be trimmed from the resulting preform to form a finished structural assembly.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application No.10/886,097, filed Jul. 7, 2004, which is a divisional of U.S. patentapplication No. 10/319,109, filed Dec. 13, 2002, now U.S. Pat. No.6,779,708, each of which is hereby incorporated herein in its entiretyby reference.

FIELD OF THE INVENTION

This invention relates to friction welding and, more specifically, tofriction welding of one or more structural members to form a structuralassembly.

BACKGROUND OF THE INVENTION

Structural devices are often formed as assemblies of a number of smallerstructural members. Such assembling of individual members may benecessary to form devices that are too large or too complicated to beformed by conventional manufacturing methods. For example, such factorsas casting sizes, forging sizes, available plate and block sizes, andthe like can limit the size and geometry of the structural members thatcan be manufactured. To form larger or more complex devices, thestructural members are typically assembled by joining the individualstructural members using a variety of known joining techniquesincluding, for example, mechanical fastening or welding.

Joints formed by mechanical fasteners such as rivets, screws, and boltstypically require an overlap of the structural materials at the joint.The fasteners and the overlap of material result in an increase inweight of the joint and the structural assembly. The joint can alsointroduce areas of increased stress, for example, around holes drilledfor receiving rivets. Alternatively, weld joints can be formed to jointhe structural members, sometimes requiring little or no overlap ofmaterial. However, the formation of conventional weld joints, such as byarc or electron beam welding, can result in undesirable dimensionalchanges in the structural members. Welding can also introduce porosityor other discontinuities into the structural members or otherwise causeunwanted changes to the material properties of the structural members.

Friction welding has also been proposed as an alternative toconventional welding methods for joining members. Linear frictionwelding, and rotational friction welding can be used to form strongjoints without reducing the mechanical characteristics of the joinedmaterials or causing significant dimensional changes. However, each ofthese conventional friction welding techniques is limited by thedimensions of the structural members and/or the joints to be formed. Forexample, conventional linear friction welding and rotational frictionwelding require one member to be moved, i.e. oscillated or rotated, andurged against the other member. Because of the difficulty of movinglarge structural members, it can be impossible or impractical to joinsome structural members by these techniques.

Thus, there exists a need for an improved apparatus and method ofjoining structural members to form structural assemblies. Preferably,the method should enable the manufacture of preforms that approximatethe desired dimensions and configuration of the structural assembly andtherefore require little machining or other subsequent processing toform the structural assemblies. The method should be adaptable forjoining large and/or complex structural members. Further, the methodshould not add significant weight to the structural assembly, and shouldminimize dimensional changes and undesirable changes to the materialproperties of the structural members.

SUMMARY OF THE INVENTION

The present invention provides an apparatus and method for joiningstructural members to form preforms and structural assemblies. A joiningmember, which can be smaller than the structural members, is frictionwelded to join the structural members. The structural members can remainstationary during the joining process and can be large or complex. Thefriction welding process provides a strong joint without appreciablydetracting from the dimensional or material characteristics of themembers. Further, the joint can be formed without an overlap of materialor other undue additions of weight.

According to one embodiment of the invention, first and secondstructural members are positioned proximately so that first and secondjoining surfaces define an angled aperture between the members. In otherembodiments, more than two structural members can be positioned todefine the aperture so that at least three members are joined. Theaperture can be a slot that extends generally uniformly through themembers or a frustoconical aperture. A joining member is urged into theslot and against the joining surfaces and moved relative to the membersto friction weld the joining member thereto. For example, the structuralmembers can be disposed substantially within a plane and the joiningmember can be urged in a normal direction generally perpendicular to theplane. The joining member can be moved alternately in first and secondopposed directions that are generally parallel to a lengthwise directionof the slot. Alternatively, the joining member can be rotated about anaxis generally collinear with a longitudinal axis of the aperture.

According to one aspect of the invention, each structural member definesa clamping portion that extends from the respective structural memberand defines a clamping surface, which can be generally parallel to thedirection of urging of the joining member. The clamping portions can beinserted in a clamping channel of a clamping device so that the clampingdevice contacts the clamping surfaces to prevent the aperture fromopening while the joining member is urged against the joining surfaces.A space can be provided between the clamping device and the joiningmember to receive flash from the joining member and the joiningsurfaces. Additional structural members can also be friction welded tothe first and second structural members to maintain their relativepositions and prevent the aperture from opening. According to anotheraspect, the structural members include alignment portions that areengaged to define an interface.

The joining member can be urged against the structural members after themotion of the joining member is terminated to form friction weld jointsbetween the joining surfaces and the joining member as the joiningsurfaces and the joining members cool. Further, the clamping portionand/or gripping portions can be trimmed from the structural and joiningmembers.

The present invention also provides a preform for use in forming astructural assembly of predetermined dimensions. The preform includesfirst and second structural members, which can be formed of aluminum,aluminum alloys, titanium, titanium alloys, steel, nickel-based alloys,copper-based alloys, or beryllium-based alloys. Each of the structuralmembers can be formed of the same or different materials, such that thepreforms and structural members formed according to the invention cancomprise a single or multiple materials. The structural members definejoining surfaces, which define an angle therebetween. A joining membercorresponding to the angle is disposed between the joining surfaces andjoined by friction weld joints to the joining surfaces. Each structuralmember also defines a clamping portion that extends from the respectivestructural member. The clamping portions define generally parallelclamping surfaces for engaging an aperture of a clamping device.According to one aspect of the invention, the joining member defines agenerally frustoconical plug and the joining surfaces define a generallyfrustoconical contour corresponding to the joining member.Alternatively, the joining member can define an elongate member and thejoining surfaces can define an angled slot that extends generallyuniformly in a lengthwise direction of the joining member andcorresponds to the joining member.

According to another aspect of the invention, the structural membersdefine alignment portions that are engaged to define an interfacetherebetween. A space between the interface of the alignment portionsand the joining member can be at least partially filled with flash fromthe joining member and/or the joining surfaces. The joining member canalso include a gripping portion that extends from between the first andsecond structural members.

According to another embodiment, the present invention provides astructural assembly that is formed from the described preform bytrimming the clamping portions of the structural members and thegripping portion of the joining member.

The present invention also provides an apparatus for joining at leasttwo structural members to form a structural assembly. The apparatusincludes a clamping device that defines a clamping aperture forreceiving at least a portion of the structural members so that thestructural members define an angled aperture for receiving a joiningmember. A connection device, configured to be connected to a joiningmember, is actuated by first and second actuators. The first actuator isconfigured to urge the connection device toward the clamping device andthereby urge the joining member into the angled aperture between thestructural members. The second actuator is configured to move theconnection device and thereby friction weld the joining member to thestructural members. The clamping device is structured to engage aclamping surface of each structural member to restrain the structuralmembers and thereby prevent the angled aperture from opening. The angledaperture can be a slot, and the second actuator can be configured tomove the connection device in first and second opposed directionsgenerally parallel to a lengthwise direction of the slot to frictionweld the joining member to the structural members. Alternatively, theaperture can be a generally frustoconical aperture, and the secondactuator can be configured to rotate the connection device about an axisgenerally collinear to the aperture to friction weld the joining memberto the structural members. The clamping device can also define a spacein the angled aperture for receiving flash from the joining member whilethe joining member is being joined to the structural members.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other advantages and features of the invention, andthe manner in which the same are accomplished, will become more readilyapparent upon consideration of the following detailed description of theinvention taken in conjunction with the accompanying drawings, whichillustrate preferred and exemplary embodiments, but which are notnecessarily drawn to scale, wherein:

FIG. 1 is a perspective view illustrating first and second structuralmembers being joined by friction welding according to one embodiment ofthe present invention;

FIG. 2 is a perspective view illustrating the structural members of FIG.1 configured before being joined;

FIG. 3 is a partial elevation view illustrating a preform formed byjoining the structural members of FIG. 1 according to one embodiment ofthe present invention;

FIG. 4 is a perspective view illustrating the preform of FIG. 3;

FIG. 5 is a partial elevation view illustrating a structural assemblyformed from the preform of FIG. 3;

FIG. 6 is a perspective view illustrating the structural assembly ofFIG. 5;

FIG. 7 is a partial elevation view illustrating first and secondstructural members joined to form a preform according to anotherembodiment of the present invention;

FIG. 8 is a partial elevation view illustrating a structural assemblyformed by trimming the preform of FIG. 7;

FIG. 9 is a perspective view illustrating two structural members joinedby three additional structural members and configured for joiningaccording to another embodiment of the present invention;

FIG. 10 is a partial elevation view illustrating a preform formed byjoining the structural members of FIG. 9 according to one embodiment ofthe present invention;

FIG. 11 is a partial elevation view illustrating a structural assemblyformed by trimming the preform of FIG. 10;

FIG. 12 is a plan view of four structural members configured for joiningaccording to another embodiment of the present invention;

FIG. 13 is a section view of a preform formed by joining the structuralmembers of FIG. 12 as seen along line 13-13 of FIG. 12;

FIG. 14 is a plan view of a structural assembly formed by trimming thepreform of FIG. 13;

FIG. 15 is a section view of the structural assembly of FIG. 14 as seenalong line 15-15 of FIG. 14;

FIG. 16 is a flow chart illustrating a method for forming a preform andstructural assembly according to one embodiment of the presentinvention; and

FIG. 17 is a flow chart illustrating a method for forming a preform anda structural assembly according to another embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention now will be described more fully hereinafter withreference to the accompanying drawings, in which preferred embodimentsof the invention are shown. This invention may, however, be embodied inmany different forms and should not be construed as limited to theembodiments set forth herein; rather, these embodiments are provided sothat this disclosure will be thorough and complete, and will fullyconvey the scope of the invention to those skilled in the art. Likenumbers refer to like elements throughout.

Referring to the drawings and, in particular, to FIG. 1, there isillustrated an apparatus 10 for joining structural members 20, 22, alsoshown in FIG. 2, by linear friction welding according to one embodimentof the invention. The structural members 20, 22 can be joined to form apreform 40, shown in FIGS. 3 and 4, that can be trimmed to form astructural assembly 50, as shown in FIGS. 5 and 6. As illustrated inFIGS. 1-4, the preform 40 is formed by joining the first structuralmember 20 and the second structural member 22 with a joining member 30.In other embodiments, the preform 40 can be formed from three or morestructural members, depending on the desired dimensions andconfiguration of the preform 40 and the structural assembly 50.

The configuration and material composition of the structural members 20,22 can be formed and selected according to the specifications and designrequirements of the structural assembly 50. The first and secondstructural members 20, 22 are illustrated in FIG. 1 as generally planarmembers, but the structural members 20, 22 can also be formed in otherconfigurations, including blocks having rectangular or squarecross-sections, tubes and cylinders having circular or ovalcross-sections, or angles or channels having a variety ofcross-sectional shapes. The structural members 20, 22 can also haveirregular geometric configurations. As is known in the art, thestructural members 20, 22 can be formed from a variety of fabricatingprocesses including milling, casting, and forging. Preferably, thestructural members 20, 22 are formed from materials having high strengthto weight ratios and good corrosion resistance. For purposes of exampleonly and not limitation, the structural members 20, 22 can comprisealuminum, aluminum alloys, titanium, titanium alloys, steel,nickel-based alloys, copper-based alloys, beryllium-based alloys, ormixtures thereof. Further, the structural members 20, 22 can be formedfrom similar or dissimilar materials.

In addition to the material composition and properties of the structuralmembers 20, 22, the selection of the structural members 20, 22 is basedon the desired dimensions of the structural assembly 50 that is to beformed. More specifically, the desired dimensions of the structuralassembly 50 can be determined first and the structural members 20, 22can then be selected so that the resulting preform 40 will closelyapproximate the predetermined dimensions and configuration of thefinished assembly 50. Advantageously, by constructing preforms 40 havingdimensions and configurations closely or substantially approximating thepredetermined dimensions and configuration of the correspondingstructural assembly 50, machining time and material waste can beminimized, making the assemblies 50 more economical to produce. Theselection of materials and the subsequent formation of preforms andstructural assemblies therefrom are described in U.S. application Ser.No. 10/092,675, titled “Preforms for Forming Machined StructuralAssemblies,” filed Mar. 7, 2002, which is assigned to the assignee ofthe present invention and the entirety of which is incorporated hereinby reference.

The apparatus and method of the present invention can be used tomanufacture various types of structural assemblies 50 that comprise partof a vehicle, such as an aircraft. For example, the structural members20, 22 can be panels, spars, beams, or other components that are joinedto form a wing, wing support structure, fuselage, and the like.

As shown in FIGS. 1 and 2, the structural members 20, 22 are configuredin the apparatus 10 so that the members 20, 22 define a slot 24therebetween. The slot 24 is partially defined by joining surfaces 21,23 of the structural members 20, 22, which are angled relative to oneanother to define a converging angle that is generally uniform along thelength of the slot 24. The joining member 30 preferably corresponds inshape to the slot 24 so that, when the joining member 30 is insertedinto the slot 24, the joining member 30 engages the joining surfaces 21,23 of the structural members 20, 22. The joining member 30 and thejoining surfaces 21, 23 of the structural members 20, 22 can define flatsurfaces as shown, or each may define a curve or other shape. Thus, thejoining member 30 and the slot 24 define a lengthwise direction, whichcan be linear or non-linear. The apparatus 10 is configured to urge thejoining member 30 in a direction 32 into the slot 24, and thereby urgethe joining member 30 against the joining surfaces 21, 23 of thestructural members 20, 22. The apparatus 10 can include a first actuator11 such as a hydraulic, pneumatic, or electric actuator for urging thejoining member 30 against the structural members 20, 22. The firstactuator 11 can be connected to a gripping portion 34 of the joiningmember 30 that extends from the slot 24 between the structural members20, 22. The first actuator 11 can be connected thereto by a variety ofconnection devices such as a hydraulically, pneumatically, ormechanically adjustable gripping device 12.

According to some embodiments of the present invention, the apparatus 10also includes a clamping device 14 that can be used to secure theposition of the structural members 20, 22 during joining. The clampingdevice 14 can define a clamping channel 16, which can extend the entirelength of the clamping device 14 or only partially therethrough.Additionally, the channel 16 can include multiple channels, which can beparallel or collinear. The channel 16 is configured to receive clampingportions 26, 28 that extend from each of the structural members 20, 22.The clamping portions 26, 28 of the structural members 20, 22 defineclamping surfaces 27, 29 that engage the clamping channel 16 and preventthe structural members 20, 22 from moving apart, i.e., opening the slot24. Thus, the engagement of the clamping surfaces 27, 29 with thechannel 16 prevents the slot 24 between the structural members 20, 22from opening and opposes the urging force of the joining member 30 intothe slot 24. If the clamping channel 16 does not extend entirely throughthe clamping device 14, the channel 16 can also prevent transversemotion of the structural members 20, 22, i.e., in directions denoted byreference numerals 38 a, 38 b. The structural members 20, 22 can besecured to the clamping device 14 by clamps 15 a, 15 b or by bolts, tackwelding, tooling, or the like. The clamping device 14 can be integralto, or connected to a backing plate 18, table, or to a device forimparting movement, such as a computer numeric control (CNC) machine orsimilar device, as is known in the art.

According to one embodiment, the structural members 20, 22 are disposedgenerally within a plane, and the urging force of the joining member 30is directed generally normal to the plane. As the joining member 30 isurged into the slot 24, the joining member 30 engages the angled joiningsurfaces of the structural members and urges the structural members 20,22 apart. The clamping surfaces 21, 23 of the structural members 20, 22engage the clamping channel 16 of the clamping device 14 and arerestrained so that the slot 24 does not open. The urging force of thejoining member 30 into the slot 24 can develop sufficient force againstthe structural members 20, 22 for linear friction welding of the joiningmember 30 to the joining surfaces 21, 23.

The joining member 30 is friction welded to the first and secondstructural members 20, 22 to form weld joints 36, 37 between the joiningsurfaces 21, 23 and the joining member 30. Friction welding isaccomplished by moving the joining member 30 relative to the structuralmembers 20, 22. The apparatus 10 can include a second actuator 13 foralternatingly moving the joining member 30 in the opposed directions 38a, 38 b, which are generally parallel to a lengthwise direction of theslot 24 and the joining member 30. For example, the second actuator 13can oscillate the joining member 30 a distance of about ⅛ inch at a rateof about 60 hertz. Other oscillation distances and frequencies can alsobe used. The second actuator 13 can be engaged to the joining member 30through the same gripping device 12 as the first actuator 11. The secondactuator 13 can be a hydraulic, pneumatic, or electric device, and insome embodiments the first and second actuators 11, 13 are an integraldevice. As the joining member 30 is urged and moved against thestructural members 20, 22, a compressive force is established betweenthe engaged surfaces of the joining member 30 and the structural members20, 22. The compressive force is typically great enough to result in apressure between the structural members 20, 22 of at least about 1000pounds per square inch, for example, about 20,000 pounds per squareinch.

The motion of the joining member 20, 22 is continued while thecompressive force is maintained resulting in friction between thejoining member 30 and the structural members 20, 22. The frictionresults in heating of the joining member 30 and the joining surfaces 21,23, which causes plasticized regions to form about the engaged surfaces.Once sufficient plasticization has occurred, the motion of the joiningmember 30 is terminated. Plasticization can be detected, for example, bymechanical or optical measurements, or friction welding can be continuedfor a predetermined duration based on such factors as the type ofmaterials being joined, the size of the joint, the compressive force,and the type of joint being formed. After the motion of the joiningmember 30 is terminated, the compressive force can be maintained bycontinuing to urge the joining member 30 into the slot 24 as the joiningmember 30 and the structural members 20, 22 cool to thereby form thefriction weld joints 36, 37.

As shown in FIG. 3, the clamping device 14 can also define an aperture17 in the channel 16 for receiving flash formed during the weldingprocess. Flash generally refers to plasticized material from the joiningmember 30 or structural members 20, 22 that is extruded from between thejoining member 30 and the structural members 20, 22 during frictionwelding due to the compressive force therebetween. The flash, generallyreferred to by reference numeral 42, can collect to form a bead ormultiple isolated deposits as illustrated in FIGS. 3 and 4. The aperture17 can be a channel-shaped groove, as shown, or one or more partial orthrough bores in the clamping device 14. As shown in FIG. 4, the flash42 can also be directed from between the joining member 30 and thejoining surfaces 21, 23 proximate to the gripping portion 34 of thejoining member 30 and longitudinally from the ends of the slot 24. Theflash 42 is typically removed when machining the preform 40 to form thestructural assembly 50.

As shown in FIGS. 3 and 4, the joining member 30 joins the structuralmembers 20, 22 to form the preform 40, which can be trimmed to form thestructural assembly 50. For example, the gripping portion 34 of thejoining member 30, the clamping portions 26, 28 of the structuralmembers 20, 22, and the flash 42 can be trimmed by any known means,including using a manual or computer-guided machining device, such as aCNC machine. For clarity of illustration, the trimmed portions are shownin unitary form in FIG. 5, but these portions are typically broken upduring trimming. Other portions of the joining member 30 and/or thestructural members 20, 22 can also be trimmed to form the structuralassembly 50. For example, as shown in FIG. 5, a portion 31 of thejoining member 30 disposed between the clamping portions 26, 28 of thestructural members 20, 22 can be trimmed. Preferably, the preform 40 istrimmed according to predetermined dimensions corresponding to a desiredconfiguration of the structural assembly 50.

The engagement of the clamping surfaces 27, 29 of the structural members20, 22 to the clamping device 14 can also facilitate an alignment of thestructural members 20, 22. For example, the clamping portions 26, 28 andthe clamping surfaces 27, 29 of the structural members 20, 22 can beconfigured so that as the clamping surfaces 27, 29 are engaged to theclamping channel 16 of the clamping device 14, the structural members20, 22 are configured in their desired configuration. Additionally, eachof the clamping portions 26, 28 of the structural members 20, 22 caninclude an alignment portion 25 a, 25 b as shown in FIGS. 7 and 8. Thealignment portions 25 a, 25 b are configured to be engaged when theclamping portions 26, 28 of the structural members 20, 22 are receivedby the clamping channel 16. Thus, as shown in FIG. 7, the alignmentportions 25 a, 25 b of the structural members 20, 22 engage to form aninterface therebetween. Preferably, when the alignment portions 25 a, 25b are engaged, the structural members 20, 22 are configured in thedesired configuration for joining. The clamping portions 26, 28 of thestructural members 20, 22 can also define a space 19 between theinterface of the clamping portions 26, 28 and the joining member 30 forreceiving the flash 42 during joining, similar to the aperture 17described above. As shown in FIG. 8, the preform 40 formed from thestructural members 20, 22 can be trimmed to remove the flash 42, thegripping portion 34, the clamping portions 26, 28, and/or other portionsof the joining member 30 and the structural members 20, 22 to form thestructural assembly 50.

While the clamping device 14 described above can be used to maintain theconfiguration of the structural members 20, 22 during friction welding,the structural members 20, 22 can also be restrained in other manners.For example, according to another embodiment of the present inventionshown in FIGS. 9-11, one or more additional structural members 60, 62,64 can be connected to the first and second structural members 20, 22 tohold the first and second structural members 20, 22 in place while thejoining member 30 is welded thereto. For example, the additionalstructural members 60, 62, 64 can be friction welded to the first andsecond structural members 20, 22 by linear friction welding, rotationalfriction welding, or friction stir welding, or the additional members60, 62, 64 can be joined by other conventional fastening methods.Similar to the clamping device 14 described above, the additionalstructural members 60, 62, 64 maintain the relative position of thefirst and second structural members 20, 22 to prevent the slot 24 fromopening when the joining member 30 is urged into the slot 24. Any numberof the additional structural members can be used, and the joining member30 can be friction welded to the additional structural members 60, 62,64 to form joints 39 therebetween such that the additional structuralmembers 60, 62, 64 preferably form part of the preform 40 and thefinished structural assembly 50. The clamping device 14 and clamps 15 a,15 b can be used to secure the structural members 20, 22, 60, 62, 64while the joining member 30 is joined thereto, as shown in FIG. 10. Forexample, the clamps 15 a, 15 b can be vise-like devices that areadjusted to hold the structural member 20, 22, 60, 62, 64 securely inplace against the clamping device 14. Alternatively, the structuralmembers 20, 22, 60, 62, 64 can be secured to the clamping device 14 bybolts, tack weld, tooling, or the like. As illustrated in FIG. 11, theflash 42, gripping portion 34, and/or other portions of the joiningmember 30 or structural members 20, 22, 60, 62, 64 can be trimmed toform the structural assembly 50.

The structural members can also be joined by other joining methods, suchas rotational friction welding, illustrated in FIGS. 12-15. In FIG. 12,four structural members 70 a-d are shown configured for joining, thoughany number of members can be joined. Each of the structural members 70a-d defines a joining surface 71 a-d, and the joining surfaces 71 a-d,are positioned to define an angled, or converging, aperture 72 betweenthe structural members 70 a-d. The aperture 72 can define a variety ofangled shapes, for example, an angled slot, as described above.Alternatively the aperture 72 can define a fristocone, or at least partof a tapered bore, as shown in FIGS. 12 and 13. As described above, eachof the structural members 70 a-d can define a clamping portion 74 a-dthat is at least partially received by a clamping device 76. Theclamping device 76 can engage a clamping surface 75 a-d of each clampingportion 74 a-d and prevent the structural members 70 a-d from movingoutward to open the aperture 72. A joining member 80 corresponds to theangle of the aperture 72 so that, as the joining member 80 is urged intothe aperture 72, the joining member 80 urges the structural members 70a-d outward from the aperture 72. The joining member 80 is then movedagainst the joining surfaces 71 a-d of the structural members 70 a-d,for example, by rotating the joining member 80 about an axis that isgenerally collinear with a longitudinal axis of the aperture 72 and thejoining member 80. The relative motion of the joining member 80 againstthe joining surfaces 71 a-d causes a frictional force therebetween,heating the joining member 80 and/or the structural members 70 a-d to aplasiticizing temperature for friction welding. When a sufficienttemperature and sufficient plasticizing have been achieved for frictionwelding, the joining member 80 is stopped. As described above, thejoining member 80 can be urged into the aperture 72 after the joiningmember 80 is stopped and until the structural members 70 a-d and thejoining member 80 cool so that a joint is formed therebetween.

As shown in FIGS. 14 and 15, a preform 84 formed by joining thestructural members 70 a-d is trimmed to form a structural assembly 86.For example, a gripping portion 82 of the joining member 80, clampingportions 74 a-d of the structural members 70 a-d, flash 81, and the likecan be trimmed from the preform 84. Additionally, as shown in FIG. 14,the clamping portions 74 a-d can be larger in combination than thejoining member 80 and the desired size of the final structural assembly86. For example, the clamping portions 74 a-d defined by the structuralmembers 70 a-d shown in FIG. 12 are larger than the joining member 80 sothat the clamping surfaces 75 a-d of the clamping portions 74 a-d candefine the aperture 72. The relatively large clamping portions 74 a-dare provided to accommodate the joining member 80. After the structuralmembers 70 a-d have been joined, the clamping portions 74 a-d and thejoining member 80 are then trimmed to achieve the desired shape and sizeof the structural assembly 86.

Referring now to FIG. 16, there are illustrated the operations forjoining structural members to form a structural assembly according toone embodiment of the present invention. A first structural member ispositioned proximate to a second structural member so that a firstjoining surface of the first structural member and a second joiningsurface of the second structural member define an angled slottherebetween. The slot is generally uniform in a lengthwise directionfor receiving a joining member therein. See Block 100. For example, thestructural members can be positioned substantially within a plane. SeeBlock 102. A clamping portion can be provided on each of the structuralmembers. Each clamping portion extends from the respective member anddefines a clamping surface. See Block 104. The clamping portions areinserted in a clamping channel of a clamping device so that the clampingdevice contacts the clamping surfaces of the structural members toprevent the slot from opening. See Block 106. A space can be providedbetween the clamping device and the joining member to receive flash fromthe joining member and the joining surfaces of the structural members.See Block 108. The structural members can also be positioned so thatalignment portions thereof are engaged to define an interface. See Block110. The structural members can also be joined to at least a thirdstructural member that maintains the relative position of the first andsecond structural members to prevent the slot from opening. See Block112. The joining member is urged into the slot and against the joiningsurfaces of the structural members. See Block 114. For example, thejoining member can be urged in a normal direction generallyperpendicular to a plane defined by the members. See Block 116. Thejoining member is moved alternately in first and second opposeddirections generally parallel to the lengthwise direction of the slot tothereby friction weld the joining member to the structural members. SeeBlock 118. For example, an actuator can be engaged to a gripping portionof the joining member to actuate the joining member in alternate opposeddirections, and the gripping portion can then be removed from thejoining member. See Block 120. The moving of the joining member isterminated, for example, after a predetermined duration of time or uponmechanical, thermal, or optical detection of sufficient plasticization.The joining member can be urged against the structural members as thejoining surfaces and the joining member cool to form the friction weldjoint therebetween. See Block 122. The clamping portions of thestructural members can then be trimmed. See Block 124.

FIG. 17 illustrates the operations for joining structural membersaccording to another embodiment of the present invention. A firststructural member is positioned proximate to a second structural memberso that a first joining surface of the first structural member and asecond joining surface of the second structural member define an angledaperture therebetween for receiving a joining member. A clamping portionof each structural member extends from the respective structural memberand defines a clamping surface. See Block 200. For example, thestructural members can be positioned so that alignment portions of eachof the clamping portions are engaged to define an interfacetherebetween. See Block 202. A space can be provided between theclamping device and the joining member to receive flash from the joiningmember and the joining surfaces of the structural members. See Block204. Further, more than two structural members can be positioned todefine the aperture so that at least three structural members are joinedto form the structural assembly. See Block 206. The clamping portions ofthe structural members are inserted in a clamping aperture of a clampingdevice. See Block 208. The joining member is urged into the aperture andagainst the joining surfaces of the structural members in a directiongenerally parallel to the clamping surfaces of the structural members sothat the joining member urges the clamping surfaces of the structuralmembers against the clamping device to thereby prevent the aperture fromopening. See Block 210. The joining member is also moved relative to thestructural members to friction welding the joining member thereto. SeeBlock 212. For example, an actuator can be engaged to a gripping portionof the joining member to actuate the joining member in alternate opposeddirections, and the gripping portion can be subsequently trimmed. SeeBlock 214. According to one aspect of the invention, the structuralmembers are positioned to define a generally uniform angled slot, andthe joining member is moved in first and second opposed directionsgenerally parallel to a lengthwise direction of the slot to frictionweld the joining member to the structural members. See Block 216.Alternatively, the structural members can be positioned to define agenerally frustoconical aperture, and the joining member can be rotatedabout an axis generally collinear with a longitudinal axis of theaperture to friction welding the joining member to the structuralmembers. See Block 218. The motion of the joining member is terminated,for example, after a predetermined duration of time or upon mechanical,thermal, or optical detection of sufficient plasticization. Afterterminating the motion, the joining member can be urged against thestructural members as the joining surfaces and the joining member coolto form the friction weld joint therebetween. See Block 220. Theclamping portion can then be trimming from the structural members. SeeBlock 222.

Many modifications and other embodiments of the invention will come tomind to one skilled in the art to which this invention pertains havingthe benefit of the teachings presented in the foregoing descriptions andthe associated drawings. For example, the structural members can beprocessed before and/or after joining by friction welding. Suchprocessing can include cleaning the joining surfaces of the structuralmembers to remove oxidation or surface defects. Additionally, thestructural members can be heat treated by aging, quenching, stretching,annealing, or solution annealing to obtain desired mechanical orchemical properties, as is known in the art. Therefore, it is to beunderstood that the invention is not to be limited to the specificembodiments disclosed and that modifications and other embodiments areintended to be included within the scope of the appended claims.Although specific terms are employed herein, they are used in a genericand descriptive sense only and not for purposes of limitation.

1. A preform for use in forming a structural assembly of predetermineddimensions, comprising: a first structural member defining a joiningsurface; a second structural member defining a joining surface, saidjoining surfaces of said first and second structural members defining anangle therebetween; and a joining member disposed between said joiningsurfaces of said structural members, said joining member correspondingto the angle defined by said joining surfaces and joined by frictionweld joints to the joining surfaces, wherein each structural memberdefines a clamping portion extending from the respective structuralmember, said clamping portions defining generally parallel clampingsurfaces for engaging an aperture of a clamping device.
 2. A preformaccording to claim 1 wherein said joining member defines a generallyfrustoconical plug and said joining surfaces define a generallyfrustoconical contour corresponding to said joining member.
 3. A preformaccording to claim 1 wherein said joining member defines an elongatemember and said joining surfaces define an angled slot extendinggenerally uniformly in a lengthwise direction of said joining member andcorresponding to said joining member.
 4. A preform according to claim 1wherein said structural members define alignment portions engaged todefine an interface therebetween.
 5. A preform according to claim 4wherein the preform defines a space between the interface of thealignment portions and the joining member, said space being at leastpartially filled with flash from at least one of the joining member andthe joining surfaces of the structural members.
 6. A preform accordingto claim 1 wherein said joining member comprises a gripping portion thatextends from between the first and second structural members.
 7. Apreform according to claim 1 wherein said structural members and saidjoining member comprise at least one of the group consisting ofaluminum, aluminum alloys, titanium, titanium alloys, steel,nickel-based alloys, copper-based alloys, and beryllium-based alloys. 8.A preform according to claim 1 wherein said joining surfaces arenonparallel and define a tapered slot therebetween, the tapered slotbeing generally uniform along a lengthwise axis of the tapered slot,such that said structural members are configured to receive said joiningmember urged into the tapered slot in a first direction to thereby urgesaid structural members apart along an axis that is perpendicular to thefirst direction.
 9. A preform according to claim 8 wherein the taperedslot has a trapezoidal cross-section that is generally uniform along thelengthwise axis of the tapered slot.